Biosynthesis tetracenomycin

Perez M, Lombo F, Zhu L et al (2005) Combining sugar biosynthesis genes for the generation of l- and D-amicetose and formation of two novel antitumor tetracenomycins. Chem Commun 12 1604—1606... 

Figure 3 Aromatic PKS gene clusters and actinorhodin biosynthesis. Partial gene clusters for the polyketides actinorhodin (act), tetracenomycin (tcm), and doxorubicin (dps) are shown. Reconstitution of combinations of act genes in a PKS clean host have led to a proposed pathway by which the early stages of actinorhodin biosynthesis occur.

W Bao, E Wendt-Pienkowski, CR Hutchinson. Reconstitution of the iterative type II polyketide synthase for tetracenomycin F2 biosynthesis. Biochemistry 37 8132-8138, 1998. 

Figure 6 Cell-free biosynthesis of tetracenomycin F2. A strain of Streptomyces glaucescens in which the tetracenomycin-minimal PKS genes and an ARO/CYC activity had been overexpressed produced tetracenomycin F2, a precursor to the natural product tetracenomycin A (the remainder of the pathway is indicated by dashed arrows). The same result has been achieved using purified proteins in vitro.

F2 was restored. More recently, the biosynthesis of tetracenomycin F2 has been achieved with fully purified proteins [17],... 

Perez M, Lombo E, Zhu L, Gibson M, Brana AF, Rohr J, Salas JA, Mendez C (2005) Combining Sugar Biosynthesis Genes for the Generation of L- and o-Amicetose and Formation of Two Novel Antitumor Tetracenomycins. Chem Conimun 1604... 

As mentioned above, iterative PKSs have been studied in detail, focusing especially on the biosynthesis of actinorhodin and tetracenomycin. Later, further genes and gene clusters have become available. In this section we describe how knowledge of the function of these enzymatic systems can be used to generate new molecules. The most important results are summarized in Figure 12.1 la and b. 

In further experiments, tcmO - a methyltransferase of the tetracenomycin cluster that methylates the C8-hydroxyl of tetracenomycin B3, an intermediate in the biosynthesis of tetracenomycin - was used to generate the new polyketide 3-O-Methyl-DMAC (59). Again, this experiment demonstrated that the variable substrate specificity of an enzyme increases its potential use in creating new molecules. 

Motamedi, H. and C.R. Hutchinson (1987). Cloning and heterologous expression of a gene cluster for the biosynthesis of tetracenomycin C, the anthracycline antitumor antibiotic of Streptomyces glaucescens. Proc Natl Acad Sci U S A 84 4445-4449. 

McDaniel, R., C.R. Hutchinson, and C. Khosla (1995) Engineered biosynthesis of novel polyketides analysis of tcmN function in tetracenomycin biosynthesis. J. Am. Chem. Soc. 117 6805-6810. 

The most well-established system for heterologous expression involves the hosts S. coelicolor or its close relative S. lividans, and a bifimctional actino-myces- . coli vector with control elements for PKS gene expression that have been derived from the actinorhodin gene cluster [59]. This host-vector system has successfuUy been used to reconstitute functionally the polyketide pathways associated with biosynthesis of frenolicin [60], tetracenomycin [59], oxytetra-cycline [61], erythromycin [62], picromycin/methymycin [63], oleandomycin... 

Using these techniques (combinatorial biosynthesis) with streptomycetes, the polyketides have now been investigated, including not only the macrolides (e. g., erythromycin) but also polycyclic aromatic compounds (e.g., actinorhodin, tetracenomycins). The formation of hybrids can alter not only the size of the poly ketide skeleton, its stereochemistry or its functionality but also enzyme systems of the later steps of biosynthesis such as, e. g., oxygenases or glycosy Itrans-ferases. In practice major difficulties arise because each intermediate in the biosynthetic sequence is a substrate for the following enzyme thus if a changed substrate is not accepted by the respective enzyme the biosynthesis breaks down. 

Elloramydn (80), like tetracenomycin, is not a candidate for commercialization. However, the polyketide biosynthesis genes for elloramycin have recently been cloned (260). As expected, the elloramydn biosynthesis gene cluster is feirly similar in mucture to the tetracenomycin biosynthesis gene cluster (260). 

Based on the currently available information, Figure 11 shows the hypothetical biosynthesis of aklanonic acid from propionyl-SCoA and malonyl-SCoA. This pathway is modified from the model proposed by Strohl and Connors (247). based on data obtained by Bartel et al. (245) and Rajgarhia and Strohl (310), using as models both tetracenomycin F2 biosynthesis by minimal tetracenomycin PKS genes (126,252-255.324) and aloesaponarin II biosynthesis by actinorhodin biosynthesis genes (245,321). 

Shen B, Hutchinson CR. Teiracenomycin FI monooxygenase Oxidation of a nafditha cenone to a naphthacenequinonc in the biosynthesis of tetracenomycin C in Streptomyces... 

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